Bi-directional buck-boost circuit

ABSTRACT

In accordance with some embodiments, a buck-boost circuit is contemplated which is bi-directional. That is, the buck-boost circuit be configured to produce a load voltage for a load responsive to a source voltage from a voltage source, and the buck-boost circuit may also be configured to produce a charging voltage for the voltage source responsive to a second voltage source connected to the load. In an embodiment, the buck-boost circuit may be operating in boost mode when providing the load voltage and may be operating in buck mode when providing the charging voltage.

PRIORITY CLAIM

This application claims the benefit of U.S. Provisional Application No.61/182,082 entitled “BUCK-BOOST CONTROL CIRCUIT” filed on May 28, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments disclosed herein may be directed to a circuit forcontrolling a buck-boost operation performed by one or more buck-boostconverters.

2. Description of the Related Art

A buck-boost converter is a DC-DC converter that typically produces anoutput voltage which is either greater than or less than the inputvoltage. The buck-boost converter may further be seen as a switch modepower supply having a similar circuit topology from individual buck andboost converters. FIG. 1 is a diagram illustrating a conventionalbuck-boost converter 100. As shown in FIG. 1, buck-boost converter 100includes a power source 102 coupled in parallel to an inductor 104, acapacitor 106, and a load 108, shown in FIG. 1 as a resistor. Buck-boostconverter also includes a diode 110 and a switch 112. In operation, whenswitch 112 is closed, voltage source 102 is directly coupled to inductor104 transferring current to inductor 104, resulting in the accumulationof energy in inductor 104, or the charging of inductor 104. As a result,capacitor 106 supplies current to load 108 and inductor 104 acts as aload as it charges, resulting in a lower output voltage. This loweroutput voltage is termed a “step-down” voltage or a “buck” voltage. Whenswitch 112 is open, as shown in FIG. 1, inductor 104 is directly coupledto load 108 and capacitor 106, and therefore current is supplied tocapacitor 106 and load 108 from inductor 104 as inductor 104 discharges,if inductor 104 has been previously charged. Inductor 104 thus acts as acurrent source, and provides a higher output voltage. This higher outputvoltage is termed a “step-up” or “boost” voltage.

Typical buck-boost converters, such as shown in FIG. 1 produce an outputvoltage having a polarity that is opposite to the polarity of the inputvoltage. In addition, the output buck voltage range may be theoreticallybetween 0 and the input voltage, and the output boost voltage may betheoretically between the input voltage and ∞. The output voltage isadjustable based on a duty cycle of a transistor which controls switch112.

Buck-boost converter 100 often requires complicated driving circuitrybecause switch 112 does not have a terminal at ground, and produces anoutput voltage which has a polarity opposite to the polarity of theinput voltage. However, these drawbacks are minimized when voltagesource 102 is a battery. As a result, buck-boost converters may often befound in battery-powered circuits to provide a variable output voltage.

Conventional buck-boost circuits, however, can not quickly be switched.Therefore, there is a need for buck-boost circuits capable of fastswitching between buck and boost modes. Conventional buck-boost circuitsusually buck or boost the input voltage to obtain a constant outputvoltage. Thus, the conventional buck-boost circuits are unidirectional.That is, the conventional buck-boost circuits buck/boost the inputvoltage to produce the output voltage but are not capable ofbucking/boosting from the output to the input. In the case that abattery is the source of the input voltage, for example, the batterycannot be charged through the buck-boost circuit. In some cases, e.g.when the battery is a Redox battery, a wide input voltage range from theRedox battery needs to be accommodated. There is also a need for abuck-boost circuit that can be controlled externally (e.g. by aprocessor).

SUMMARY OF THE INVENTION

In accordance with some embodiments, a buck-boost circuit iscontemplated which is bi-directional. That is, the buck-boost circuitmay be configured to produce a boost voltage on a Bbus responsive to asource voltage from a voltage source on Cbus. The buck-boost circuit mayalso be configured to produce a charging (buck) voltage for the voltagesource on the Cbus responsive to a second voltage source connected tothe Bbus. In an embodiment, the buck-boost circuit may be operating inboost mode when providing the boost voltage and may be operating in buckmode when providing the charging voltage.

In accordance with some embodiments, a buck-boost circuit may controlthe output voltage (load or charging) in a range from 0 through the fullvoltage supported in the system. The buck-boost circuit may, in anembodiment used with a flow cell battery, may provide plating currentsat the low voltages desired for plating, for example. A controller suchas a processor executing software that monitors the buck-boost circuitor hardware monitor circuitry may provide a control input to thebuck-boost circuit, which may modify a feedback voltage to the buckand/or boost controllers to change the output voltage. For example, thefeedback voltage may be shifted with respect to ground. In anembodiment, the response of the output voltage to the control input maybe rapid. In an embodiment, a controller such as a processor or monitorhardware may monitor the current produced from the buck-boost circuitand may use the control input (which may be a voltage) to increase ordecrease the total current available to the output (load or chargingcurrent), to produce a desired amount of output current.

In some embodiments, the buck-boost circuit may implement multiplebuck-boost converters in parallel. The buck-boost circuit may thisemploy redundancy, whereby a failure of one or more of the buck-boostconverters does not prevent continued operation of the system. Forexample, a buck-boost converter may include one or more fuses to preventirreparable damage to the buck-boost converter in the event ofovercurrent conditions or other malfunctions. If a fuse blows, thebuck-boost converter no longer operates until the fuse is replaced.However, other buck-boost converters may still be in operation and maypermit the system to continue functioning. A controller (e.g. softwareexecuting on a processor or hardware) may cause the other buck-boostconverters to produce additional current through control inputs to thebuck-boost converters. In an embodiment, the controller may monitor apeak voltage over the inductor in the buck-boost converters to detect afailure in a converter.

In an embodiment, the buck-boost circuit is designed to withstand inrushcurrents that are significantly larger than the currents that thebuck-boost circuit is designed to handle during normal operation. Theinrush currents may occur during power up of the system, duringinsertion of the buck-boost circuit into a system that is in operation,etc. In an embodiment, the buck-boost circuit implements surge currentsupply circuit that provides the surge current. An exemplaryimplementation of the surge current supply circuit may include one ormore polyfuses applied in parallel to bypass the surge current aroundthe buck-boost circuit. The polyfuses may bypass the large surgecurrents, and may heat and eventually open as the surge current isdissipated. The buck-boost circuit may subsequently begin normaloperation.

In an embodiment, the buck-boost circuit described herein achieves highefficiency in the conversion. The efficiency may be measure as theamount of power on the output for a given amount of source power. Forexample, efficiencies in the range of about 94-95% may be achieved inboost mode. Efficiencies in the range of about 96-97% in buck mode maybe achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention will become apparent to thoseskilled in the art with the benefit of the following detaileddescription of embodiments and upon reference to the accompanyingdrawings in which:

FIG. 1 is a diagram depicting a conventional buck-boost converter;

FIG. 2 is a diagram depicting a redox flow cell of a redox flow cellbattery;

FIG. 3 is a diagram illustrating a particular example of a flow cellbattery system according to some embodiments;

FIG. 4 is a diagram of one embodiment of a state function map foroperation by a controller system;

FIG. 5 is a diagram illustrating a buck-boost circuit;

FIG. 6 is a diagram illustrating the external control interface ingreater detail for an embodiment;

FIG. 7 is a diagram illustrating a buck-boost converter; and

FIGS. 8A-8G, 9A-9I, and 10A-10F are a circuit diagram illustrating oneembodiment of the buck-boost circuit of FIG. 5 and the buck-boostconverter of FIG. 7 in greater detail.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Thedrawings may not be to scale. It should be understood, however, that thedrawings and detailed description thereto are not intended to limit theinvention to the particular form disclosed, but to the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the present invention as definedby the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is to be understood the present invention is not limited toparticular devices or methods systems, which may, of course, vary. It isalso to be understood that the terminology used herein is for thepurpose of describing particular embodiments only, and is not intendedto be limiting. As used in this specification and the appended claims,the singular forms “a”, “an”, and “the” include singular and pluralreferents unless the content clearly dictates otherwise.

Reference will now be made in detail to embodiments disclosed in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

One embodiment of the buck-boost circuit is described below in thecontext of a flow cell battery system. However, buck-boost circuitssimilar to those described herein may be used in numerous otherapplications and are not limited to the use described below. Controllercircuitry such as the processor-based design illustrated in some of thefigures herein or a hardware-based design may be used with variousembodiments of the buck-boost circuit in such other applications. Anoverview of the flow cell battery system is discussed next.

Flow Cell Battery and System Overview

FIG. 2 illustrates a redox flow cell 200 of a redox flow cell batteryaccording to some of the embodiments described herein. As shown, cell200 includes two half-cells 208 and 210 separated by a membrane 206. Anelectrolyte 224 is flowed through half-cell 208 and an electrolyte 226is flowed through half-cell 210. Half-cells 208 and 210 includeelectrodes 202 and 204 respectively, in contact with electrolytes 224and 226, respectively, such that an anodic reaction occurs at thesurface of one of electrodes 202 or 204 and a cathodic reaction occursat the surface of the other one of electrodes 202 or 204. In someembodiments, multiple redox flow cells 200 can be electrically coupled(e.g., stacked) either in series to achieve higher voltage or inparallel in order to achieve higher current. As shown in FIG. 2,electrodes 202 and 204 are coupled across load/source 220, through whichelectrolytes 224 and 226 are either charged or discharged. The operationof a flow cell and the composition of a membrane is further described inU.S. patent application Ser. No. 12/217,059, entitled “Redox Flow Cell,”filed on Jul. 1, 2008, which is incorporated herein by reference.Construction of a flow cell stack is described in U.S. patentapplication Ser. No. 12/577,134, entitled “Common Module Stack ComponentDesign” filed on Oct. 9, 2009, which is incorporated herein byreference.

When filled with electrolyte, one half-cell (e.g., 208 or 210) of redoxflow cell 200 contains anolyte 226 and the other half-cell containscatholyte 224, the anolyte and catholyte being collectively referred toas electrolytes. Reactant electrolytes may be stored in separate tanksand dispensed into the cells 208 and 210 via conduits coupled to cellinlet/outlet (I/O) ports 212, 214 and 216, 218 respectively, often usingan external pumping system. Therefore, electrolyte 224 flows intohalf-cell 208 through inlet port 212 and out through outlet port 214while electrolyte 226 flows into half-cell 210 through inlet port 216and out of half-cell 210 through outlet port 218.

At least one electrode 202 and 204 in each half-cell 208 and 210provides a surface on which the redox reaction takes place and fromwhich charge is transferred. Suitable materials for preparing electrodes202 and 204 generally include those known to persons of ordinary skillin the art. Examples of electrodes 202 and 204 are also described inU.S. patent application Ser. No. 12/576,235, entitled “Magnetic CurrentCollector” filed on Oct. 8, 2009, which is incorporated herein byreference. Redox flow cell 200 operates by changing the oxidation stateof its constituents during charging or discharging. The two half-cells208 and 210 are connected in series by the conductive electrolytes, onefor anodic reaction and the other for cathodic reaction. In operation(i.e., charge or discharge), electrolytes 226 and 224 (i.e., anolyte orcatholyte) are flowed through half-cells 208 and 210 through I/O ports212, 214 and 216, 218 respectively as the redox reaction takes place.Power is provided to a load 220 or received from power source 220,depending on if the flow cell battery is in discharging or chargingmode, respectively.

FIG. 3 illustrates a flow cell battery system 300 in which a flow cellbattery 312 can operate according to some embodiments. As shown in FIG.3, power is received from several sources, including an external powerline 352 or a generator 354 (e.g., a diesel or gas powered generator).In general, external power can be received from any source, including apower grid or dedicated generator 352 such as a solar, tidal, wind, orother form of generator 352. AC power is received in a rectifier 302,which is coupled to provide DC power to load 364. DC power is providedto flow cell battery system 300 from rectifier 302 when AC power issupplied to rectifier 302. In the embodiment shown in FIG. 3, DC powersupplied to flow cell battery system 300, and to load 364, is suppliedbetween a reference bus and a Bbus.

As shown in FIG. 3, flow cell battery system 300 includes a flow cellbattery 312, which includes a flow cell stack 322 and a rebalance cell328. Flow cell stack 322 provides or receives DC power through a Cbus toa buck-boost circuit 310. An example of buck-boost circuit 310 isdescribed in more detail below. During charging of flow cell battery 312from the external source, buck-boost circuit 310 provides chargingcurrent from rectifier 302 to flow cell stack 322 in order to chargeflow cell battery system 300. During discharge, buck-boost circuit 310provides power across load 364 when no power is provided by rectifier302. Power is supplied or received by buck-boost circuit 310 whenswitches 366 are closed.

Specifically, in an embodiment, the buck-boost circuit 310 may operatein buck mode (or may be “bucking”) during charging of the flow cellbattery 312 and may operate in boost mode (or may be “boosting”) duringdischarge of the flow cell battery 312 to the load. Thus, the buck-boostcircuit 310 is bi-directional in this embodiment

Rebalance cell 328 is coupled to flow cell stack 322 to rebalance theelectrolytes during operation. Rebalance cell 328 is controlled by arebalance control board 320. Some embodiments of rebalance cell 328 andrebalance control board 320 are further described in U.S. patentapplication entitled “Flow Cell Rebalancing”, filed concurrentlyherewith, which claims priority to U.S. Provisional Patent ApplicationNo. 61/182,099 entitled “Flow Cell Rebalancing”, filed May 28, 2009,both of which are incorporated herein by reference. As shown in FIG. 3,when switch 368 is closed, power can be supplied to rebalance cell 328by rebalance control board 320.

Monitor and control circuit 330 monitors and controls operation of flowcell battery system 300. As shown in FIG. 3, monitor and control circuit330 is coupled to rebalance control board 320 and the buck-boost circuit310, and monitors the Bbus and the Cbus. Monitor and control circuit 330is also coupled to control the flow of electrolytes in flow cell stack322. Specifically, with regard to the buck-boost circuit 310, themonitor and control circuit 330 may monitor the circuit 310 and mayprovide control to the circuit 310. The monitor and control circuit 330may, in an embodiment, include one or more processors. At least one ofthe processors may execute code that performs the monitoring and controlof the circuit 310. In other embodiment, the monitor and control circuit330 may include hardware that performs the monitoring and control.

FIG. 4 illustrates a state diagram that can be executed on monitor andcontrol circuit 330 for operation of flow cell battery system 300. Asshown in FIG. 4, monitor and control circuit 330 starts in shutdownstate 401. In state 401, all pumps are off and all buck-boosts are off.Sensor monitoring is on and monitor and control circuit 330 may besampling data. Further, a genset request may be on. Essentially, flowcell battery system 300 is off. Switches 366 and 368, as shown in FIG.3, may be open, isolating flow cell battery system 300 from load 364, asshown in FIG. 3.

Monitor and control circuit 330 transitions to a system initializationstate 402 when a main switch, switch 366, is turned on or a shortcondition is experienced for a specified period of time. In someembodiments, switch 368 is closed along with switch 366. Ininitialization state 402, load 364 is available and flow cell batterysystem 300 is powered on. Further, software parameters are initialized.Once initialization step 402 is complete, monitor and control circuit330 transitions to plating step 403.

During plating state 403, power is applied across the electrodes of flowstack 322 (shown in FIG. 3) in order to provide plating of theelectrodes using a plating metal added to the electrolytes for theelectrodes in flow stack 322 (e.g., bismuth metal). In some embodiments,a small current at a nominal voltage is provided. When the current dropsbelow a current threshold value or the voltage increases above a voltagethreshold value, plating is completed. For example, in some embodimentsthe plating voltage is set at 16.25 V with a current of 8 amps. Platingis completed if the current drops below 4 amps and the voltage increasesabout 16.75 volts. Once plating is completed, monitor and controlcircuit 330 transitions to charging state 404.

In some embodiments, especially when a new flow cell battery 312 isplaced in service, a small amount of plating metal is added to theelectrolytes and is plated onto the electrodes of flow cell stack 322during plating state 403. When flow cell stack 322 has been plated, insome embodiments plating state 403 can be bypassed. In some embodiments,plating state 403 operates on each transition from initialization state402. Plating is done at low voltage and low current. In order thatplating state 403 completes, even with systems that have already beenplated, monitor and control circuit 330 is capable of detectingcompletion in order to transition to charging state 404.

Several states of state machine 400 transition to shutdown state 401upon detection of a fault. Fault conditions include, for example,detection of a leak, detection of a high temperature situation,detection of a pump problem, detection of a power supply failure forpowering electronics, and detection of a low electrolyte level. Otherfault conditions may also be detected. Monitor and control circuit 330transitions from plating state 403 to shutdown state 401 upon detectionof a fault or if a buck state in buck-boost circuit 310 is not enabled.

In charging state 404, flow cell battery 312 is charged. Generally,charging involves supplying a current to the flow cell battery 312 whileflowing electrolytes through flow cell stack 322 in order to restore thecharged chemical state of the electrolytes. Charging electrolytes isgenerally discussed in U.S. application Ser. No. 12/074,110, filed onFeb. 28, 2008, which is incorporated herein by reference.

In the charge state 404, power is supplied from either generator 354 orpower source 352 through rectifier 302. In some embodiments, voltage onthe Bbus when rectifier 302 is active can be about 54 V. Buck-boostcircuit 310 is in buck mode and provides power to C-bus, which isutilized to charge flow cell stack 322. Pump controls are active tocontrol pumps for the flow cell battery, the level sensors are active tomonitor electrolyte levels in tanks for the battery, state-of-chargemonitoring is active, and thermal control is on.

Further, the state of charge (“SOC”) of the electrolytes are monitoredand reported during the charging process. Descriptions of measurementsof the state of charge is provided in U.S. patent application Ser. No.11/674,101, filed on Feb. 12, 2007, which is herein incorporated byreference. During charging, thermal monitoring and control isaccomplished, for example as U.S. patent application Ser. No.12/577,127, entitled “Thermal Control of a Flow Cell Battery” filed onOct. 9, 2009, which is incorporated herein by reference.

In some embodiments, a particular voltage and current are applied to theelectrodes in order to charge the electrolytes. Applying power to theelectrodes while electrolytes flow through the flow cell battery bringsat least a portion of the electrolytes from a discharged chemical stateto a charged chemical state. In some embodiments, charging may stop at apredetermined charged set point. For example, charging may be stoppedwhen the SOC reaches substantially 100%. In other embodiments, thepredetermined charged set point is reached when an SOC is greater than80%, greater than 85%, greater than 90%, greater than 95%, or greaterthan 99%. If, at that time, power from power source 352 is stillavailable, monitor and control circuit 330 transitions to a float state405. In some embodiments, for example, charging may occur at a voltageacross the electrodes of about 30 volts and a current through flow cellstack 322 of about 100 amps, although more complicated chargingalgorithms can be employed by monitor and control circuit 330.

If a fault is detected during the charge process that occurs in chargestate 404, monitor and control circuit 330 transitions to shutdown state401 to shut system 300 down. Otherwise, once a SOC of about 100% isachieved, monitor and control circuit 330 transitions to float state 405if buck is still enabled. Monitor and control circuit 330 transitionsfrom charge state 404 to discharge state 406 if buck-boost 310 switchesfrom buck to boost, indicating that power is no longer being receivedfrom rectifier 302.

During float state 405, buck is enabled and provides an output voltageat a particular value. In some embodiments, the value is about 25 Volts.During this state, flow cell battery 312 is standing by and ready toprovide power to load 364 should power at rectifier 302 be reduced.During the float state, the pump control is on and pumps may be run toprovide a small flow of electrolyte through flow cell stack 322.Further, in some embodiments, power utilized for providing voltage onbuck-boost 310 and for running pumps and other system may be supplied bycharging rectifier 302 instead of drawing on the charged electrolyte ofbattery 312. Further, monitoring of the SOC can be turned off. Again, ifa fault is detected, monitor and control circuit 330 transitions to shutdown state 401.

If power to rectifier 302 fails, then monitor and control circuit 330transitions from float state 405 to discharge state 406. Monitor andcontrol circuit 330 can also transition from charge state 404 todischarge state 406 before SOC is about 100% if the signal en_boostindicates that power to rectifier 302 has been interrupted. In dischargestate 406, power from flow cell battery 312 is supplied to load 364. Inthat case, the pumps are activated and controlled, buck-boost circuit310 is in boost mode, electrolyte levels in the tanks are monitored, andthe SOC is monitored and reported. In some embodiments, the Bbus voltagecan be held at about 50 V. Once the SOC drops below a certain value, forexample 10%, or available power on the Cbus drops, for example belowabout 20 V, which indicates that flow cell battery 312 is in asubstantially discharged state, then monitor and control circuit 330 cantransition from discharge state 406 to a hibernation state 407. If,during discharge, a fault is detected, then monitor and control circuit330 can transition from discharge state 406 to shutdown state 401.Further, if power, for example from power source 352 or from generator354, is supplied to rectifier 302 then monitor and control circuit 330can transition from discharge state 406 back to charge state 404,buck-boost circuit 310 switches from boost mode to buck mode, so thatflow cell battery 312 can be recharged.

Monitor and control circuit 330 transitions into hibernate state 407from discharge state 406 when flow cell battery 312 is reaches apredetermined discharged set point. For example, the flow cell batterysystem 300 may be transitioned to a hibernation state when the SOC isless than 1%. In other embodiments, the predetermined discharged setpoint is reached when an SOC is less than 20%, less than 15%, less than10%, less than 5%, or less than 2%. In hibernate state 407, the pumpsare off and buck-boost 310 is turned off. Monitor and control circuit330 monitors flow cell battery system 300 until the charge on flow cellstack 322 is depleted. Monitor and control circuit 330 can transitionedout of hibernate state 407 if power returns to rectifier 302, in whichcase monitor and control circuit 330 transitions to charge state 404 torecharge flow cell battery 312. Monitor and control circuit 330 can alsotransition from hibernate state 407 to shutdown state 401 if a faultcondition is detected.

Monitor and control circuit 330 can transition from hibernate state 407if power appears on the Bbus. In some embodiments, generator 354 may beactivated in discharge state 406 if SOC is reduced below a thresholdlevel. In some embodiments, generator 354 may be activated in hibernatestate 407.

In handling any fault state that occurs throughout state machine 400,the first fault can be latched for later review and state machine 400transitions to shutdown state 401. In some cases, multiple cascadingfault conditions result from the initial fault condition, so capturingthe first fault condition can help a servicer to restart system 300.

Buck-Boost Circuit

The Bbus and the Cbus referred to herein may each be a power bus, orpower input/output, to which the buck-boost circuit 310 is coupled. Thebuck-boost circuit 310 is bi-directional in some embodiments, and thusmay supply power (voltage and current) on either power input/output at agiven point in time. As described previously, the buck-boost circuit 310may operate in buck mode to supply power on the Cbus, and may operate inboost mode to supply power on the Bbus. In other embodiments, the buckand boost modes may be reversed. In general, the buck-boost circuit 310may be configured to operate in buck mode to supply power to one powerinput/output and in boost mode to supply power to another powerinput/output.

FIG. 5 illustrates an embodiment of a buck-boost circuit 310. As shownin FIG. 5, buck-boost circuit 310 is coupled to the flow cell battery312 which is coupled to a surge current supplier 504. Surge currentsupplier 504 may be one or more thermal polyfuses, such as a RUEF 400thermal fuse manufactured by Tyco Electronics or any equivalent fuse.Battery 312 is also coupled to current sensing circuit 506. Currentsensing circuit 506 is coupled to control circuit 508 and currentlimiter circuit 510. Consistent with some embodiments, control circuit508 may be coupled to the monitor and control circuit 330 so as totransmit and receive signals from circuit 310 to the monitor and controlcircuit 330. Specifically, the control circuit 508 may transmit signalsto be monitored by the monitor and control circuit 330, and may receivecontrol input signals to control the operation of the circuit 310.Consistent with some embodiments, current limiter circuit 510 mayinclude a hot swap controller which is capable of allowing a circuit tobe safely inserted and removed from a live power source, and in thisapplication allows for the momentary high currents involved in switchingoperations. Current limiter circuit 510 further may include a shortcircuit detection feature, a current limiting feature, and anovervoltage protection feature. According to some embodiments, currentlimiter circuit 510 may include an LT 4256-3 Hot Swap™ controller fromLinear Technology Corporation. The controller protects the buck-boostcircuit 310 during high current events.

In operation, when the initial voltage is applied from input voltagesource 312, a current surge is created and flows into surge currentsupplier 504. Surge current supplier 504, therefore, allows themomentary high current that occurs initially when buck-boost 514 isfirst switched. As the current flows through surge current supplier 504,surge current supplier 504 heats up until surge current supplier 504reaches a predetermined temperature. When surge current supplier 504reaches the predetermined temperature, surge current supplier 504 tripsand opens, current is no longer able to flow through surge currentsupplier 504. Surge current supplier 504 will remain tripped until surgecurrent supplier 504 cools down below the predetermined temperature.

Current limiter circuit 510 and current sensing circuit 506 detect thetripped condition and enable current to flow through current limitercircuit 510. Current limiter circuit 510 allows current flow betweenbattery 312 and buck-boost converters 514. In an embodiment, currentlimiter circuit 510 has a predetermined current limit, and if thecurrent flowing through current limiter circuit exceeds thepredetermined current limit, the current limiter circuit 510 latchesoff. Current sensing circuit 506 senses the current and control circuit508 outputs the current to the monitor and control circuit 330. Themonitor and control circuit 330 may determine that the current hasfallen back below the predetermined limit, and the monitor and controlcircuit 330 may transmit a latch release signal to current limitercircuit 510, to enable current limiter circuit 510.

The control circuit 508 is further coupled to a buck-boost ON/OFFcircuit 512. Buck-boost ON/OFF circuit 512 receives a buck enable signalbuck_en from monitor and control circuit 330 and a boost enable signalboost_en from the monitor and control circuit 330 through controlcircuit 508, and passes the appropriate signal to the plurality ofbuck-boost converters 514. However, to prevent one buck-boost converter514 from bucking while another buck-boost converter 514 is boosting, andto make sure that all of the buck-boost converters 514 are performingthe same buck or boost operation, buck-boost ON/OFF circuit 512 receivesthe buck enable and boost enable signals from an external controllercoupled to control circuit 508, and outputs an assertion of at most oneof the buck enable or boost enable signals at a time. In effect,buck-boost ON/OFF circuit 512 acts as an exclusive-OR so that buck-boostcircuits 514 are either off, in a buck mode, or in a boost mode. In someembodiments, buck-boost ON/OFF 512 receives a buck_en signal and aboost_en signal and provides corresponding signals to buck-boostconverters 514. If buck_en is the same as boost_En (i.e., both on orboth off), then the signals provided to buck-boost converters 514 areoff. If buck_en is on and boost_en is off, then the signals provided tobuck-boost converters 514 turn buck mode on. If buck_en signal is offand boost_En is on, then the signals provided to buck-boost converters514 turn boost mode on.

As shown in FIG. 5, circuit 310 includes three (3) buck-boost convertercircuits 514 coupled in parallel. Buck-boost converters 514 may becoupled to the monitor and control circuit 330 through control circuit508 in order to measure characteristics of buck-boost converters 514, asis explained further below. The use of three buck-boost convertercircuits 514 allows for greater flexibility in controlling output power.The output of all of the buck-boost converter circuits 514 may becombined to produce a power that may be unobtainable with only onebuck-boost converter circuit 514.

Moreover, using more than one buck-boost converter circuit 514 alsoprovides redundancy, such that if one buck-boost converter circuit 514fails, the other circuits can still produce a desired output power. Inthe illustrated embodiment, three buck-boost converter circuits 514provide redundancy. In other embodiments, additional or fewer buck-boostconverter circuits 514 may be used to provide a desired level ofredundancy.

In boost mode, buck-boost converter circuits 514 receive the voltagefrom current limiter circuit 510, and boost the voltage, depending onthe boost_en signal received from buck-boost ON/OFF circuit 512. Theboosted voltage is output through nodes 516 across capacitor 518, whichrepresents a load circuit. In buck mode, voltage is applied betweennodes 516 and the bucked voltage and current is supplied to battery 312.In an embodiment, buck-boost converters 514 all have the same referencecurrent to enable current sharing of buck-boost converters 514.Buck-boost converter circuits 514 are discussed in further detail below.

Consistent with some embodiments, surge current supplier 504, currentsensing circuit 506, current limiter 510 and buck-boost converters 514may be arranged on a single circuit board and coupled to battery 312,control circuit 508, and buck-boost ON/OFF circuit 512. Furtherconsistent with some embodiments, battery 312, control circuit 508, andbuck-boost ON/OFF 512 circuits may be coupled to a plurality of circuitboards including surge current supplier 504, current sensing circuit506, current limiter 510 and buck-boost converters 514. This may allowmultiple buck-boost stages for controlling the magnitude of an outputvoltage. The use of multiple circuit boards each having buck-boostcapability allows for further redundancy and extra failsafes in case onecircuit board should fail. In some embodiments, circuit 310 produces apulse-width modulated output having a low frequency and non-synchronoustiming.

FIG. 6 is a block diagram illustrating an interface between thebuck-boost circuit 310 and the monitor and control circuit 330 ingreater detail consistent with some embodiments. The interface mayinclude one or more signals provided by the buck-boost circuit 310 tothe monitor and control circuit 330 for monitoring. For example, theremay be a section detect signal 606 for each buck-boost converter 514,indicating whether or not that buck-boost converter 514 is operational.There may be one or more voltage monitor signals 608 (e.g. a voltagemonitor signal for each of the Bbus and the Cbus). The voltage monitorsignal may be the voltage on the corresponding bus, or may be a voltagederived from the voltage on the bus. For example, a resistor dividernetwork may divide down the voltage on the corresponding bus to providea voltage for monitoring that may be lower than the voltage on thecorresponding bus. There may also be one or more current monitor signals610 (e.g. from the current sensing circuit 506) indicating the currentthat has been detected in the buck-boost circuit 310. In someembodiments, additional current monitor signals may provided external tothe buck-boost circuit 310, to monitor the current provided on the Bbusand/or Cbus. The external current monitor signals may be desired, e.g.,when more than one buck-boost circuit 310 is provided in parallel foradditional redundancy and/or more current capacity. It is noted that thesignals provided for monitoring in this embodiment are merely exemplaryof one embodiment, and other embodiments may provide additional signals,or other signals, as desired in other embodiments.

The monitor and control circuit 330 also provide various control inputsto the buck-boost circuit 310. For example, the monitor and controlcircuit 330 may provide the buck_en and boost_en signals previouslydiscussed. The buck_en signal may be asserted to indicate buck mode andthe boost_en signal may be asserted to indicate boost mode. In the statemachine 400 shown in FIG. 4, for example, the boost_en signal may beasserted in the discharge state 406. The buck_en signal may be assertedin the charge state 404, the plating state 403, and the float state 405.Additionally, the monitor and control circuit 330 may control thevoltage output in the buck mode (to the flow cell battery 312)differently in different states. For example, in the plating state 403,the monitor and control circuit 330 may control the voltage on the Cbusto be closer to zero than the charge state 404 and the float state 405.A voltage on the order of 16.25 volts and a current of about 8 amps maybe desired, as mentioned above. The voltage provided on the Cbus may beadjusted using the feedback adjust control voltage (buck_v 616 in FIG.6). The buck_v voltage may change the feedback voltage on from the Cbusprovided to the buck circuitry, which may change the voltage output bythe buck circuitry 616 correspondingly. Additionally, the latch_releasesignal to the current limiter circuit may be provided (reference numeral614) by the monitor and control circuit 330.

In the embodiment shown, the monitor and control circuit 330 may includea processor 600 configured to execute control code 604 stored in amemory 602 to which the processor 600 is coupled. The control code 604may, in general, monitor samples of the output signals captured byhardware within the monitor and control circuit 330 from the buck-boostcircuit 310 (and potentially other circuitry in the flow cell batterysystem 300) and may generate the control inputs to the buck-boostcircuit 310 (and potentially other circuitry in the flow cell batterysystem 300). Any control code 604 may be implemented in variousembodiments. In one embodiment, the control code 604 may implement thestate machine 400 shown in FIG. 4. As mentioned previously, the monitorand control circuit 330 may also implement control of the buck-boostcircuit 310 in hardware.

The memory 602 may be one embodiment of a processor-accessible storagemedium configured to store instructions to be executed by a processor.Generally speaking, a processor-accessible storage medium may includeany storage media accessible by a processor during use to provideinstructions and/or data to the processor. For example, a processoraccessible storage medium may include storage media such as magnetic oroptical media, e.g., disk (fixed or removable), tape, CD-ROM, orDVD-ROM, CD-R, CD-RW, DVD-R, DVD-RW, or Blu-Ray. Storage media mayfurther include volatile or non-volatile memory media such as RAM (e.g.synchronous dynamic RAM (SDRAM), double data rate (DDR, DDR2, DDR3,etc.) SDRAM, low-power DDR (LPDDR2, etc.) SDRAM, Rambus DRAM (RDRAM),static RAM (SRAM), etc.), ROM, Flash memory, non-volatile memory (e.g.Flash memory) accessible via a peripheral interface such as theUniversal Serial Bus (USB) interface, etc. Storage media may includestorage media accessible via a communication medium such as a networkand/or a wireless link.

FIG. 7 illustrates an embodiment of buck-boost converter 514. As shownin FIG. 7, inductor 706 is serially coupled to resistor 708. A buckswitch 710 and a boost switch 712 is coupled between resistor 708 andterminal 516. Diodes 716 and 718 are coupled in parallel to switches 710and 712, respectively. As shown in FIG. 7, a buck controller 702controls buck switch 710 and a boost controller 704 controls boostswitch 712. Buck controller 702 activates buck switch 710 when buck_enis on and boost controller 704 controls boost switch 712 when boost_enis on. A buck_V signal controls the voltage generated by buck-boostconverter 514 during buck mode. A Sync signal is provided as a timingsignal to buck controller 702 and boost controller 704. In anembodiment, buck controller 702 and boost controller 704 may receive acurrent feedback from resistor 708. As shown in FIG. 7, each of thethree buck-boost converters 514 can be provided with a sync signal thatis phased such that each is 120 degrees out of phase. A voltage acrossthe inductor 706 (Section DET) can be provided indicating theperformance of the buck boost circuit 514 to the control circuit 508,which may generate corresponding section detect signals 606 to themonitor and control circuit 330. The section detect signals 606 may thusindicate whether or not buck-boost converter 514 is operating.Buck-boost circuit 514 may also include a feedback control circuit formodifying a buck feedback voltage to the buck controller 702 using thebuck_V voltage, to control the voltage generated during buck operation.

In an embodiment, a fuse may be provided for each buck-boost converter514, or for each buck-boost circuit 310. The fuse may be in series withthe inductor 706 and may blow if the buck-boost converter fails. Thus,the current in the inductor 706 may drop to zero when the fuse blows andthe failure of the buck-boost converter 514 may be detected by measuringthe Section DET voltage (at peak). The failure of the buck-boostconverter 514 does not affect the performance of other buck-boostconverters 514, or other buck-boost circuits 310 which may be coupledtogether.

Accordingly, some embodiments as disclosed herein may provide abuck-boost circuit which provides a rapid switch between buck operationsand boost operations. Some embodiments as disclosed herein may alsoprovide short circuit protection of a buck-boost converter using acontroller. Some embodiments as disclosed herein may provide buck-boostcontrol wherein a feedback voltage to the buck control and the boostcontrol are lifted from a ground to provide a faster response. Moreover,some embodiments as disclosed herein may provide buck-boost controlhaving added redundancies for safety and bi-directional functionality.

FIGS. 8A-8G, 9A-9I, and 10A-10F illustrate a circuit diagram of oneembodiment of the buck-boost circuit 310 in greater detail. Portions ofthe circuit diagram that correspond to the components illustrated inFIGS. 5, 6, and 7 are illustrated and numbered on the diagram. Thecontrol circuit 508 may generally include various circuitry illustratedacross FIGS. 8A-8G, 9A-9I, and 10A-10F. Accordingly, portions of thecircuit diagram that correspond to portions of the control circuit 508are indicated with the numeral 508 with a letter postfixed thereon.

FIGS. 8A-8G illustrate the surge current supplier 504 as two polyfusesin parallel (see dash-boxed elements labeled 504 in FIGS. 8A-8G). Otherembodiments may include more or fewer polyfuses in any parallel orseries combination as desired. The current sensing circuit 506 (dashedbox labeled 506 in FIG. 8A-8G) is also illustrated, generating currentmonitoring signals 610 (labeled LCI_C_(—)1 and LCI_D_(—)1 in FIGS.8A-8G). The current limiter circuit 510 is illustrated in FIGS. 8A-8G(dashed box labeled 510). As mentioned previously, if the currentlimiter circuit 510 has latched off, the latch_release signal 614 may beasserted to enable the buck-boost circuit 310 again. In someembodiments, the transistor controlled by the latch_release signal maybe considered part of the control circuit 508. In other embodiments, thetransistor controlled by the latch_release signal may be considered partof the current limiter circuit 510 and the latch_release signal may beprovided directly to the current limiter circuit 510 as illustrated inFIG. 5.

A set of three amplifier circuits 508A may receive the voltages measuredacross the inductors 706 of each buck-boost converter 514 and maygenerate the section detect signals 606 (labeled BTSI1, BTSI2, and BTSI3in FIGS. 8A-8G). Additionally, a current amplifier 508B is illustratedin FIGS. 8A-8G, coupled to receive the buck_V voltage 616 and to providecurrent drive capability on an output node 800 in FIGS. 8A-8G. Theoutput node 800 is used in the buck-boost converters 514 discussed inmore detail below. A voltage generator 508C is provided to generate a 12volt voltage based on the Bbus and Cbus voltages.

FIGS. 9A-9I illustrate two of the buck-boost converters 514, and a thirdbuck-boost converter 514 is illustrated in FIGS. 10A-10F. The componentsof one of the buck-boost converters 514 are labeled to correspond withFIG. 7, and similar components are included in the other buck-boostconverters 514. Specifically, the buck controller 702 and the boostcontroller 704 are illustrated in FIGS. 9A-9I. In this embodiment, eachcontroller may include an LT3845 High Voltage Synchronous Current ModeStep-Down Controller available from Linear Technology Corporation. TheLT3845 does not output voltages as high as the Bbus and Cbus can reach,and thus an LTC4444 high voltage driver 802 may be used to increase thevoltage levels as needed. The buck on switch 710 and boost on switch 712are implemented as transistors in the illustrate embodiment, each inparallel with a diode 716 and 718. The inductor 706 and current feedbackresistor 708 are also illustrated.

In buck mode, current flows from the Bbus to the Cbus to charge the flowcell battery 312. Additionally, buck-boost converter 514 is attemptingto produce a specified voltage on the Cbus during the charging activity(depending on whether the state machine is in plating state 403,charging state 404, or floating state 405, for example). Accordingly,the feedback voltage to the buck controller 702 is provided from theCbus (reference numeral 900). In particular, the feedback voltage 900 istapped from a resistor divider network including resistors 902. In thisembodiment, 4 resistors are used having exemplary values 2.32 kilo-ohms(kohms), 2 kohms, 10 kohms, and 120 ohms from top to bottom in FIGS.9A-9I. Any number of resistors and values may be used in variousembodiments, providing a known ratio of the buck feedback voltage to theCbus voltage.

As mentioned previously, the buck_v control voltage may be used toadjust the feedback voltage provided to the buck controller 702, tocontrol the voltage on the Cbus. The output node 800 from FIGS. 8A-8Gare coupled to another resistor 904 (exemplary value 100 ohms in thisembodiment) to inject additional current into the resistor dividerformed from resistors 902. The effect is to increase the feedbackvoltage to the buck controller 702 (reference numeral 900) when thebuck_v voltage is increased. Accordingly, the monitor and controlcircuit 330 may provide voltage control to the buck-boost circuit 310,and the buck-boost circuit 310 may provide current control internallyresponsive to the voltage control.

Similarly, the feedback voltage for the boost controller 704 is measuredfrom the Bbus (since that is the output voltage in boost mode in thisembodiment), indicated at reference numeral 906. A resistor dividernetwork from the Bbus may be used to scale the feedback voltage 906 aswell. In other embodiments, a boost_v voltage to adjust the boostfeedback voltage may be implemented if desired, similar to the buck_vvoltage discussed above.

FIGS. 9A-9I also illustrates the voltage monitor signals 608 for theBbus and Cbus (reference numeral 608A and 608B in FIG. 9A-9I, labeledBSTVI_(—)1 and CELVI1, respectively). In this embodiment, the monitorvoltages are also scaled via resistor divider networks.

The sync signal generator 508D is also illustrated in FIGS. 9A-9I. Thesync signal generator 508D may generate the Sync signals for eachbuck-boost converter 514. In the illustrated embodiment, the sync signalgenerator 508D comprises an LTC6902 Multiphase Oscillator available fromLinear Technology Corporation.

FIGS. 10A-10F illustrate the third buck-boost converter 514, as well asthe buck-boost on-off circuit 512. The circuit 512 is coupled to receivethe buck_en and boost_en signals 612, and asserts (low) shutdown signalsto each buck controller 702 and boost controller 704 responsive to thesignals. Particularly, if both buck_en and boost_en are assertedconcurrently, the circuit 512 may shut down all controllers 702 and 704.Otherwise, if the buck_en signal is asserted and the boost_en isdeasserted, the shutdown signals to the buck controllers 702 aredeasserted and the shutdown signals to the boost controllers 704 areasserted, establishing buck mode. If the boost_en signal is asserted andthe buck_en signal is deasserted, the shutdown signals to the boostcontrollers 704 are deasserted and the shutdown signals to the buckcontrollers 702 are asserted, establishing boost mode. If both buck_enand boost_en signals are deasserted, all shutdown signals may beasserted and the circuit 310 may be idle.

In this patent, certain U.S. patents, U.S. patent applications, andother materials (e.g., articles) have been incorporated by reference.The text of such U.S. patents, U.S. patent applications, and othermaterials is, however, only incorporated by reference to the extent thatno conflict exists between such text and the other statements anddrawings set forth herein. In the event of such conflict, then any suchconflicting text in such incorporated by reference U.S. patents, U.S.patent applications, and other materials is specifically notincorporated by reference in this patent.

Further modifications and alternative embodiments of various aspects ofthe invention will be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the invention. It is to beunderstood that the forms of the invention shown and described hereinare to be taken as examples of embodiments. Elements and materials maybe substituted for those illustrated and described herein, parts andprocesses may be reversed, and certain features of the invention may beutilized independently, all as would be apparent to one skilled in theart after having the benefit of this description of the invention.Changes may be made in the elements described herein without departingfrom the spirit and scope of the invention as described in the followingclaims.

What is claimed is:
 1. A buck-boost circuit comprising: a first voltagebus; a second voltage bus; at least one buck-boost converter coupledbetween the first voltage bus and the second voltage bus; wherein: thebuck-boost converter is configured to generate a voltage on the firstvoltage bus responsive to a voltage on the second voltage bus in a firstmode of operation during use; the buck-boost converter is configured togenerate the voltage on the second voltage bus responsive to the voltageon the first voltage bus in a second mode of operation during use; thefirst mode of operation is a boost mode; the second mode of operation isa buck mode; and the buck-boost converter comprises: an inductor; afirst node; a first switch in parallel with a first power diode betweenthe second voltage bus and the first node, wherein the first switch isconfigured to be closed in the buck mode and the first power diode isdistinct from the first switch; and a second switch in parallel with asecond power diode between the first node and ground, wherein the secondswitch is configured to be closed in the boost mode and the second powerdiode is distinct from the second switch; and a monitoring circuitconfigured to: monitor a voltage across the inductor; and detect afailure of the buck-boost converter, wherein the failure of thebuck-boost converter is indicated when a peak voltage across theinductor is zero.
 2. The buck-boost circuit as recited in claim 1further comprising a buck controller configured to generate a firstcontrol signal to the first switch, wherein the first switch isconfigured to be open or closed responsive to the first control signal.3. The buck-boost circuit as recited in claim 2 wherein the buckcontroller is coupled to receive a feedback voltage generated by afeedback circuit responsive to the voltage on the second voltage busduring use, and wherein the feedback circuit is coupled to receive anadjustable control signal and is configured to modify the feedbackvoltage responsive to the control signal.
 4. The buck-boost circuit asrecited in claim 3 wherein the buck controller is configured to change amagnitude of the voltage on the second voltage bus responsive to thefeedback voltage, and wherein the modification of the feedback voltagecauses the buck controller to modify the voltage on the second voltagebus during use.
 5. The buck-boost circuit as recited in claim 1 whereinthe monitoring circuit is further configured to generate a failuresignal to indicate the failure in response to the peak voltage of zero.6. The buck-boost circuit as recited in claim 1 further comprising acurrent limiter circuit configured to limit a current to the buck-boostconverter to a defined maximum value.
 7. The buck-boost circuit asrecited in claim 6 wherein the current limiter circuit is configured tolatch off if the current to the buck-boost converter reaches the limit,and wherein the current limiter circuit is coupled to receive a latchrelease signal configured to cause the current limiter circuit to enablefrom being latched off, and wherein the monitoring circuit is configuredto generate the latch release signal.
 8. The buck-boost circuit asrecited in claim 1, further comprising a surge current circuit coupledin parallel with the buck-boost converter, wherein the surge currentcircuit is configured to supply current during a power on event on oneof the first voltage bus and the second voltage bus during use, whereinthe surge current circuit comprises at least one polyfuse.
 9. Thebuck-boost circuit as recited in claim 8 wherein the at least onepolyfuse increases in temperature when supplying the surge currentduring use, and wherein the polyfuse is configured to create an opencircuit in response to reaching a predetermined temperature during use.10. The buck-boost circuit as recited in claim 1 wherein the first powerdiode is a power Schottky rectifier and the second power diode is apower Schottky rectifier.
 11. A buck-boost circuit comprising: a firstvoltage bus; a second voltage bus; at least one buck-boost convertercoupled between the first voltage bus and the second voltage bus; and asurge current circuit coupled in parallel with the buck-boost converter;wherein: the buck-boost converter is configured to generate a voltage onthe first voltage bus responsive to a voltage on the second voltage busin a first mode of operation during use; the buck-boost converter isconfigured to generate the voltage on the second voltage bus responsiveto the voltage on the first voltage bus in a second mode of operationduring use; the first mode of operation is a boost mode; the second modeof operation is a buck mode; the surge current circuit is configured tosupply current during a power on event on one of the first voltage busand the second voltage bus during use; the surge current circuitcomprises at least one polyfuse; and the buck-boost converter comprises:a first node; a first switch in parallel with a first power diodebetween the second voltage bus and the first node, wherein the firstswitch is configured to be closed in the buck mode and the first powerdiode is distinct from the first switch; and a second switch in parallelwith a second power diode between the first node and ground, wherein thesecond switch is configured to be closed in the boost mode and thesecond power diode is distinct from the second switch.
 12. Thebuck-boost circuit as recited in claim 11 further comprising a buckcontroller configured to generate a first control signal to the firstswitch, wherein the first switch is configured to be open or closedresponsive to the first control signal.
 13. The buck-boost circuit asrecited in claim 12 wherein the buck controller is coupled to receive afeedback voltage generated by a feedback circuit responsive to thevoltage on the second voltage bus during use, and wherein the feedbackcircuit is coupled to receive an adjustable control signal and isconfigured to modify the feedback voltage responsive to the controlsignal.
 14. The buck-boost circuit as recited in claim 13 wherein thebuck controller is configured to change a magnitude of the voltage onthe second voltage bus responsive to the feedback voltage, and whereinthe modification of the feedback voltage causes the buck controller tomodify the voltage on the second voltage bus during use.
 15. The buckboost circuit as recited in claim 11, further comprising a monitoringcircuit configured to detect a failure of the buck-boost converter. 16.The buck-boost circuit as recited in claim 15 wherein the buck-boostconverter further comprises an inductor, and wherein the monitoringcircuit is configured to monitor a voltage across the inductor.
 17. Thebuck-boost circuit as recited in claim 11 further comprising a currentlimiter circuit configured to limit a current to the buck-boostconverter to a defined maximum value.
 18. The buck-boost circuit asrecited in claim 17 wherein the current limiter circuit is configured tolatch off if the current to the buck-boost converter reaches the limit,and wherein the current limiter circuit is coupled to receive a latchrelease signal configured to cause the current limiter circuit to enablefrom being latched off, and wherein the monitoring circuit is configuredto generate the latch release signal.
 19. The buck-boost circuit asrecited in claim 11 wherein the at least one polyfuse increases intemperature when supplying the surge current during use, and wherein thepolyfuse is configured to create an open circuit in response to reachinga predetermined temperature during use.
 20. The buck-boost circuit asrecited in claim 1 wherein the first power diode is a power Schottkyrectifier and the second power diode is a power Schottky rectifier.